Field
Aspects of the present disclosure relate to air-to-ground communication systems, and more particularly to an air-to-ground communications system adapted for use with an airborne mobile platform that provides a low cost high performance aircraft antenna.
Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. Such networks may be terrestrial-based networks. However, in recent years, publicly accessible networks are being made available for passengers on commercial air transportation, e.g., airplanes and other aircraft.
Such services may be referred to as air-to-ground (ATG) communication services, and may provide such services as broadband data, voice communication, and entertainment such as streaming movies or music. Although ATG services and networks are similar to currently deployed terrestrial cellular and other wireless networks, there are aspects of ATG networks that differ from these networks.
As aircraft fly across a geographic region, each aircraft may be serviced by a particular base transceiver station (BTS) until signal quality, signal strength, or available bandwidth from that BTS is insufficient, at which time service is transferred to another BTS. Such a transfer may be referred to a “handoff,” similar to handoffs that occur in terrestrial cellular networks for cellular devices (handsets, PDAs, etc.) when such devices are mobile.
Aircraft may use a single transceiver having an antenna mounted on the undercarriage of the aircraft to communicate with the BTS. However, BTS antenna patterns are usually designed to service terrestrial customers. The beam patterns at a given BTS are usually not arranged to service ATG communications traffic.
Current generation satellite communications systems offering broadband internet service to commercial jetliners specify sophisticated high gain agile beam antennas to initiate and maintain the communications link to the satellites. These antennas may be large, complex, and expensive, and involve large surface areas and volumes on the aircraft fuselage, adding to installation costs.
Capacity for these systems is limited, and launching new satellites to accommodate capacity growth can be prohibitively expensive. Generally, these costs are passed on to the consumer in the form of higher service fees.
Merely replicating terrestrial cellular beam patterns or satellite antenna beam patterns around the aircraft in an omnidirectional pattern would provide insufficient signal strength and capacity to service the thousands of aircraft and potentially hundreds of thousands of users in such an ATG system. The omnidirectional pattern also creates interference patterns that could be deleterious to communications links in ATG systems as well as other aircraft communications systems.
As aircraft travel through a particular BTS service area, or are handed off to another BTS service area, the aircraft antenna may also change beam patterns or beam directions to provide continuous service during aircraft flight, which may not have as stringent tracking accuracy as with satellite communications links. Federal Communication Commission (FCC) rules may also prohibit certain portions of the flight from providing communications services. FCC rules may prevent transmissions in specific terrestrial directions which may not have been at issue when the transmissions were directed to higher elevations. Further, aircraft flight characteristics, and aircraft fuselage shape and antenna mounting possibilities, may make aircraft antenna design for ATG systems meeting FCC and system user specifications difficult.